1. Field Of The Invention
The present invention relates to devices for protecting light sensitive objects and systems from the damaging effects of high intensity light and, more particularly, to an optical switch which is capable of rapid semiconductor-to-metal phase transition to provide frequency agile protection against pulsed laser light having pulsewidths ranging from under a nanosecond to microseconds and operating in the far infrared spectral region.
2. Description Of The Prior Art
There has been an increasing need for the development of effective devices for protecting light sensitive objects such as the eyes of military personnel and the detector elements of electro-optical (EO) equipment and systems from the damaging effects of laser radiation, particularly in military applications where there has been increased deployment of lasers as offensive weapons for disabling personnel and systems that rely on EO equipment. Military applications of lasers in the visible (400 to 700 nm) and near-infrared (700 to 1200 nm) spectral region are already well known and numerous protective devices to counter these laser threats have been proposed and developed. In these applications, protective eyewear has been developed for the protection of the eyes of military personnel. Military use of lasers has now advanced into the far infrared spectral region (8 to 12 .mu.m) for which there are presently few, if any, viable protective measures.
In order to be effective, the protective device must allow the object that it protects, whether it be a detector or sensor of an EO system or a person's eyes, to operate over a broad range of wavelengths until irradiated with a light at an intensity above the level at which damage to the object occurs. It is also usually beneficial if the protective device remains transparent when there is no laser threat to allow the protected object to operate unimpaired. More importantly, the protective device must have a rapid response time after being irradiated above the damage threshold to effectively attenuate the incidental light. In many applications, a response time of a few nanoseconds is necessary to prevent temporary or permanent damage to the protected object.
While numerous devices have been developed to protect against high intensity light generated by lasers or a nuclear flash, most lack the ability to remain transparent over a broad wavelength range and still be capable of attenuating high intensity light within a few nanoseconds. Some devices are capable of performing one of the above-mentioned functions but are generally inadequate in performing other necessary functions.
In the case of laser light, particularly frequency agile pulsed laser light in the 8 to 12 .mu.m spectral region with pulse-widths ranging from nanoseconds to microseconds, there are few, if any, viable counter measures that are now available. Potential devices that can possibly be used to block this particular type of laser light with a response time in the order of nanoseconds have experienced problems with thermal biasing or require materials or thin films that are difficult to obtain or manufacture.
It would be advantageous to have a device or switch that provides adequate protection against pulsed laser light in the far infrared spectral region (8 to 12 .mu.m) and that will remain transparent to incident light having an intensity below the damage threshold of the protected object It would be additionally advantageous for the device to have a response period of a few nanoseconds in order to protect against damage from short pulses of laser light having pulsewidths from nanoseconds to microseconds. Such a device would have numerous applications especially if it can be easily manufactured in a relatively simple lightweight structure.